drm/i915: Initialise mmaped_count for i915_gem_object_info

Reported-by: 0day kbuild test robot
Fixes: 2bd160a1 ("drm/i915: Reduce i915_gem_objects to only show...")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1471263496-27537-1-git-send-email-chris@chris-wilson.co.uk


Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>